A rotary offset printing press includes a folding machine which cuts a web into pieces of a predetermined length and folds the web in a width direction and in a length direction, after the web is printed by a print unit and dried and cooled by a drying and cooling unit (see, for example, Patent Literature 1).
Folding methods implemented by the folding machine include: former folding for folding a web before being cut in two in a width direction by a former; single-parallel folding for folding a signature cut from the web in two in a length direction between a folding cylinder and a first jaw cylinder; double-parallel folding (folding in four) for further folding the single-parallel folded signature in two in the length direction between the first jaw cylinder and a second jaw cylinder; delta-folding (rolling folding) for firstly folding a signature, at a one-third position in a width direction, in two in the length direction between the folding cylinder and the first jaw cylinder and then further folding the signature in two in the length direction between the first and second jaw cylinders; and chopper folding for folding the single-parallel folded, double-parallel folded or delta-folded signature in two in a direction parallel to a conveying direction of the signature by use of a chopper. These folding methods are selected to be used independently or in combination according to the specification of the signature.
Meanwhile, the signature to be chopper-folded by the chopper in the folding machine described above is conveyed to stoppers of the chopper while being held between each of multiple pairs of conveying belts, the pairs being provided at intervals in a direction perpendicular to the conveying direction.
However, since the signature is folded in the direction parallel to the conveying direction of the signature by a former located upstream of the chopper, the signature has two sides, in the direction parallel to the conveying direction, one of which is thick and the other of which is thin. Therefore, these two sides of the signature slip at different degrees on the conveying belts. As a result, the signature may be conveyed to the stoppers in a tilt state and may be obliquely folded by the chopper. Moreover, multiple stoppers are provided at intervals in the direction perpendicular to the conveying direction of the signature. Thus, when a signature made of weak paper is conveyed at a high speed, a portion of the signature striking against corners of the stoppers may be torn or scratched.